2.-Department of Cytology, Institute for Biological Research Siniša Stanković, University of Belgrade, 142 Despot Stefan Blvd.,
Belgrade, Republic of Serbia

3.-Department of Physiology and Biochemistry, Institute of Biology, Faculty of Natural Sciences and Mathematics, Ss Cyril and
Methodius University in Skopje, Arhimedova 3, Skopje, Republic of Macedonia

4.-Ministry of Education, Science and Technological Development of the Republic of Serbia, Njegoševa 12, Belgrade,
Republic of Serbia

2.-Department of Cytology, Institute for Biological Research Siniša Stanković, University of Belgrade, 142 Despot Stefan Blvd.,
Belgrade, Republic of Serbia

3.-Department of Physiology and Biochemistry, Institute of Biology, Faculty of Natural Sciences and Mathematics, Ss Cyril and
Methodius University in Skopje, Arhimedova 3, Skopje, Republic of Macedonia

4.-Ministry of Education, Science and Technological Development of the Republic of Serbia, Njegoševa 12, Belgrade,
Republic of Serbia

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Abstract

Objective

As a consequence of global warming, the increase in the average annual temperature is observed, while
the living organisms actively adapt to these changes. High environmental temperature initiates numerous physiological,
autonomic, and behavioral responses, and activates the stress response. Thus, the aim of the study was to investigate
effect of a moderate increase in ambient temperature on the activity of the hypothalamic-pituitary-adrenocortical (HPA)
axis by determining histological changes in adrenal glands and hormonal levels in adult male rats.
Material and Methods: In this experimental study, the morpho-functional state of adrenal glands was estimated by
stereological evaluation of parameters, including the adrenal volume, adrenocortical cell/nuclear size and number, and
the volume density of vascular tissues after four days of exposure to a moderate increase in ambient temperature of
35 ± 1˚C. Novelli histochemical and vascular endothelial growth factor (VEGF) immunohistochemical staining provided
insight into the adrenal gland vascular network. Additionally, the adrenal levels of aldosterone, corticosterone, and
pituitary adrenocorticotropic hormone (ACTH) were determined as crucial indicators of the hypothalamic-pituitary-
adrenocortical (HPA) axis activity.

Results

Prolonged exposure to a moderate increase in ambient temperature for four days resulted in a significant
increase in ACTH level up to 24%, which altered adrenal glands both structurally and functionally. The adrenocortical
volume and number of cells in all cortical zones were markedly increased (P<0.05). A statistically significant increase
was shown in the level of aldosterone (16%) and corticosterone (25%) in serum levels of individuals.

Conclusion

Increased activity of the HPA axis reflects the response to a moderate increase in ambient temperature
during four days, showing the capacity of the HPA axis to adapt the organism to daily temperature changes.